1. Field of the Invention
This invention relates to a vibration wave driven motor, especially to a type of motor in which a resilient member formed with a traveling vibration wave therein is press-contacted to a rail-like stator and the resilient member moves along the side of a rail-like stator or a printer utilizing such kind of vibration wave driven motor.
2. Related Background Art
FIGS. 11 and 12 show examples of a conventional vibration wave driven motor.
1 indicates the resilient member made of metal having a contact surface with projections 1a, which is formed with multiple slits (not indicated in figure). Joined with the resilient member is a piezoelectric element 2 divided into multiple sectors grouped as A and B, whereon several ten KHz alternating current voltage is applied to form a traveling vibration wave. Although detailed explanation of the principle and composition for the piezoelectric element 2 is eliminated here as these belong to the prior arts, the traveling vibration wave is generated by applying alternating current voltage having a 90 degree time phase over a driving piezoelectric element comprised of two groups (A, B) disposed with 90 degrees positional phase therebetween. 8 is the rail-like stator affixed to base plate 10 of the motor case and making a friction contact with resilient member 1 under effect of a spring 3 by way of a vibration absorber 5, a piece of felt for example.
6A is a comb-teeth type stopper. The comb-teeth 6Aa are inserted into the slits (not indicated in the figure) of the opposite side of resilient member 1 which does not contact with the rail-like stator 8, and support the resilient member 1 by way of felt 7 placed on a bottom of said slit by said comb teeth 6Aa.
The resilient member 1 is supported by a table plate 4 by ways of stopper 6A, pressurized spring 3 etc. The table plate 4 is supported by a restraint member 9 which restrains movement other than the predetermined direction B.sub.Y.
When a traveling vibration wave is formed on the resilient member 1, a friction produced between the rail-like stator 8 and the resilient member 1 causes the resilient member to move on the rail-like stator 8 and subsequently the table plate 4 and other elements such as 3, 5, 6A, 7 also move in the direction B.sub.Y along the restraint member 9. Simultaneously, the generated friction drive force will effect a part of the resilient member and the part is deviated from the supporting position, a momentum force is created on the resilient member which causes the resilient member to slide away in the directions of B.sub.X and B.sub.Y.
The comb-teeth 6Aa of stopper 6A are inserted into the slits of resilient member 1 as shown in FIG. 12 thereby restraining the resilient member's movement towards B.sub.Y direction and at the same time supporting its weight by way of the felt 7. The restraint members 6B and 6C restrain the deviation of the resilient member in the direction B.sub.X and the restraint member 6D restrains the pressurized side of resilient member 1 in the direction B.sub.Y. Thus supported by these elements 6A through 6D, the resilient member 1 can make a smooth and straight movement without wobbling along with the table plate 4.
As disclosed in U.S. Pat. Nos. 4,723,129 and 4,740,796, this type of motor is used as an actuator of a printer head for bubble jet type in which the printer head is installed on a carriage (not indicated in figure) of the top plate 4, thereby enabling the head to make a straight forward and backward motions.
However, the foregoing example entailed a shortcoming in which the resilient member 1 becomes unstable and tilted towards the direction A in FIG. 11. It is because the thickness of felt 7 supporting said resilient member changes with a lapse of time.
This shortcoming of the vibration wave apparatus also resulted in a low quality of printing.